Turbines are widely used in a variety of aviation, industrial, and power generation applications to perform work. Each turbine generally includes alternating stages of peripherally mounted stator vanes and axially mounted rotating blades. The stator vanes may be attached to a stationary component such as a casing that surrounds the turbine, while the rotating blades may be attached to a rotor located along an axial centerline of the turbine. The stator vanes and rotating blades each have an airfoil shape, with a concave pressure side, a convex suction side, and leading and trailing edges. A working fluid, such as steam, combustion gases, or air, flows along a gas path through the turbine. The stator vanes accelerate and direct the compressed working fluid onto the subsequent stage of rotating blades to impart motion to the rotating blades, thus turning the rotor and performing work.
Various conditions may affect the maximum power output and/or efficiency of the turbine. For example, higher power levels and lower ambient temperatures increase the differential pressure of the compressed working fluid across the turbine. At higher differential pressures, the compressed working fluid may reach supersonic velocities as it passes through the turbine, creating considerable shock waves and reflected shock waves between adjacent rotating blades and corresponding shock losses at the trailing edge of the rotating blades. At a sufficient differential pressure, the shock waves become tangential to the trailing edge, creating a condition known as limit load. The strong shock now goes from the trailing edge of one airfoil to the trailing edge of the adjacent airfoil. The resultant shock waves and corresponding shock losses may limit the maximum power output of the turbine as the maximum tangential force is reached. If the pressure ratio increases beyond the limit load, a drastic increase in loss occurs. Conversely, at lower power levels, the shock reflection from the pressure side onto the suction side of the airfoil occurs farther upstream. At a sufficiently low pressure ratio, the shock reflection becomes normal, thus leading to high loss and corresponding reduction in turbine efficiency. As a result, the maximum power output of the turbine may be limited by colder ambient temperatures. Therefore, an airfoil and method for reducing shock losses and/or enhancing turbine efficiency at lower power levels would be useful.